Range expansion mechanisms of the invasive kelp Undaria pinnatifida

Species invasions in marine habitats have dramatically increased in the last decades. This thesis revealed characteristics of the invasive kelp Undaria pinnatifida that support its invasive potential along various phases of the invasion process. Experiments, including morphological, physiological and biochemical analyses, explored traits of different life history stages. The kelp displayed broad physiological tolerance to the tested abiotic factors (desiccation, temperature, salinity). Based on its capability to survive extended periods of air exposure, overland transport is proposed as an invasion vector for U. pinnatifida. With regard to elevated temperatures the invader outperformed native kelps, indicating a competitive advantage in a warming ocean. Observations of simultaneously developing gametophytes revealed the occurrence of inter-specific interactions at microscopic stages. Interactions of U. pinnatifida and Macrocystis pyrifera resulted in an enhancement of the invader's performance.